Technical requirements for washing bottles, flasks, etc, for containing beverages or food products should guarantee not only cleaning thereof, but also removal and elimination of germs and bacteria which may affect the products to be packed. To this end, it is basic that, at least one of the caustic soda solution tanks into which bottles are immersed be at a temperature of about 65.degree. C. and that the machine guarantees, at its maximum operating speed, the permanence of the bottle into such tank during a minimum predetermined period of time.
Present washing machines, those having a single immersion tank as well as those having several tanks, have independent heating elements and temperature control elements for each tank which, requiring a stepwise control of the temperature in order that the thermal change when glass bottles pass from one tank to the other do not cause breakage thereof.
Operation at raising temperature step or steps offers no problems, but when operating at decreasing temperature steps, the heat released from containers and bottles when passing from a high temperature tank to one of lower temperature gradually heat the lower temperature tank, thus requiring its continuous drainage replacing the cold solution in order to maintain temperature levels. As a consequence, the energy delivered to the raising temperature tanks, generally by means of water steam, is lost when draining the tanks in the cooling step.
Another disadvantage of known washing machines is the lack of temperature uniformity in each of the tanks which, due to their large volume, do not permit temperature distribution at the same rate through the whole liquid mass and, although mechanical stirrers comprised by swivelling plates are sometimes used, a local turbulence is only attained in a small region of the tank. Thus, the maximum temperature required by standards is not attained during the proper period of time.